Self-loading .[.auger.]. scrapers .Iadd.with a conveyor, such as an auger, .Iaddend.have complex hydraulic systems with a large number of controls at the operator's cab, and in order to minimize the complexity of the operation it is desirable to combine controls where it is practical to do so. The operator must, of course, be able to move the scraper bowl between an elevated road position and a lower loading and unloading position. There is also a control for the bowl apron which closes the front of the bowl when a load is being transported and which is moved for loading and unloading. The auger must operate during loading, and in the case of a fixed auger must also operate during unloading. There is also a pitch and bounce control which should be operative when the unit is in transport mode but which must be locked out for loading and unloading.
U.S. Patent 3,311,389 discloses a system for control of pitch and bounce in tractor-trailer combinations, referred to herein as a cushion hitch. U.S. Patent 3,618,984 discloses a pilot selector valve for simultaneously controlling separate fluid circuits of a device such as a self-loading scraper. The pilot selector valve of Patent 3,618,984 permits a single manual valve control handle to control the operation of two operating circuits which are essentially separate; and is disclosed in that patent as simultaneously controlling the locking out of a cushion hitch and the operation of a push-pull coupling control circuit for tandem machines as disclosed in U.S. Patent 3,469,861.
Patent 3,618,984 discloses a manually controlled three position pilot selector valve which has a first position in which the cushion hitch is operative for controlling pitch and bounce of the tractor and trailer during transport, either loaded or unloaded; a second position in which the cushion hitch is locked in a lowermost position to provide a rigid connection between the tractor and trailer for loading and unloading; and a third position in which the cushion hitch is still locked down, and in addition the push-pull coupling is actuated to tie two tractors together in tandem.